This invention relates to discharge tubes and more particularly but not exclusively to metal vapour discharge tubes for use in metal vapour lasers.
In metal vapour laser discharge tubes the active medium of the tube is constituted, at least in part, by a metal vapour such as for example copper or lead in a buffer gas of, say, neon or helium. In previous discharge tubes of this type the metal, which is to be vaporised to form part of the active medium of the tube, is inserted in fragmented form into the tube prior to its operation. During operation of the tube a discharge is initially established in the buffer gas and the heat of the discharge causes the metal fragments to vaporise. However, problems may arise in such a conventional tube. The metal fragments may be deposited onto the laser windows when the laser is shipped and may enter the vacuum pump during evacuation of the system or pumping during laser operation. Also, molten metals can have deleterious effects on insulating surfaces of the tube. Another problem is that when the metal fragments have melted, conducting paths of random length and geometry are formed along the interior insulating surfaces of the tube, which can have undesirable effects on its operation as a laser, discharge tube or spectral source.